ABSTRACT: Alzheimer disease (AD) is the most common form of dementia in older individuals. Both genetic and environmental factors contribute to AD risk, yet despite huge research efforts, a significant portion of the genetic etiology of AD remains unexplained. Population-wide studies of unrelated AD cases and controls have identified several common genetic risk factors and through the Alzheimer?s Disease Sequencing Project (ADSP) whole exome (WES) and whole genome sequencing (WGS) data are being analyzed to identify AD risk modulators. However, the primary focus of almost all of these studies has been on identifying variants that increase risk; studies designed to identify variants that may protect from AD are few and usually underpowered. Thus, additional strategies are required to identify functional variants that protect against or delay the development of AD. The Amish provide a powerful and unique opportunity to identify variants protecting against AD whilst controlling for some confounding factors such as level of education, lifestyle and diet. In addition, the large Amish pedigrees offer an enrichment strategy for identifying rare variants since Mendelian transmissions from parents to offspring, coupled to inbreeding loops, maximize the chance that multiple copies of rare variants exist. The primary goal of this project is to identify genetic variations offering protection against AD. The project will achieve this goal by pursuing three specific aims: (1): Generation of a family-based Amish AD Protective Variant dataset. We will collect DNA and phenotype data from Amish families in Ohio and Indiana by examining and following 800 known and newly identified cognitively normal individuals age 80+ and their 1st and 2nd degree relatives. We will perform SNP genotyping on all samples and WGS on a subset of 200 cognitively normal individuals; (2): Identification of AD protective variants. Sibships with multiple individuals who are age 80+ and cognitively normal will be analyzed for genetic linkage, IBD segment sharing, and association. Single-marker analyses will be supplemented by gene-wise analysis and pathway (gene set-based) analysis; (3): Perform functional validation of candidate protective variants. These experiments will include screening for effects on gene expression, impact on A? or tau processing, and effects on cellular function.